Correct tire sizes?
 

I have a 2011 Mustang Gt. It's been lowered 1.25 in the rear with Steeda Sport Springs. Koni shocks adj Pandhard bar. Question is I just bought 20x11 shelby rims I'm planning on using 315x35x20s just wanted too know if this gonna work my rims are a +55 offset.

duplicate post is not going to get you a better or quicker answer; it will only fragment the thread

Here is mine with 295/35 19 on a 19X10 47.5 offset wheel Lowered .8/1.2
https://cimg4.ibsrv.net/gimg/themust...12dd4e1d4b.jpg
https://cimg5.ibsrv.net/gimg/themust...ffd7bf5277.jpg
With your set up I think you are going to have to trim the bump off the inner wheel well, I think I have about 1/2 inch between the tire and the inner wheel well and by the offset calculator it is .7 inches further in and the backspacing is . 8 more.